1. Field of the Disclosure
The present invention relates generally to integrated circuits, and more particularly, the present invention is related to integrated circuits that operate in applications where high voltages may be present between terminals of the integrated circuit.
2. Background
Integrated circuits for power supplies, motor drives, light emitting diode (LED) lighting, and similar applications typically operate with high voltage applied between at least two terminals of the integrated circuit. The voltage may vary between zero and several hundred volts, and the terminals may be exposed to positive and negative polarities. To meet requirements for small size and low cost, nearly all the components within the integrated circuit must be designed for much lower voltages. In a typical example, the internal circuits may operate at less than 6 volts, and they may be damaged if they are exposed to more than 9 volts. Therefore, integrated circuits may have components that operate with relatively low voltage as well as components that must operate with relatively high voltage.
The terminals of some integrated circuits that operate at high voltage may be only the terminals of a controlled switch, whereas other terminals may need to sense a high voltage rather than just switch a high voltage. For example, it may be necessary for the integrated circuit to sense when the high voltage falls to a relatively low threshold value, or for example when the voltage changes polarity. Such sensing may be required to detect zero-crossings of ac voltages for timing purposes, or the sensing may be required to detect impending negative voltage for the purpose of activating protective clamp circuits.
The task of sensing is much more difficult than the task of switching, particularly when the sensing must be fast and accurate. An economical solution is needed for integrated circuits to detect with speed and accuracy the event of a voltage at a high-voltage terminal reaching a relatively low threshold value.
Corresponding reference characters indicate corresponding components throughout the several views of the drawings. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.